Medical endoscopic probes have the ability to provide images from inside a patient's body. Considering the potential damage to a human or animal body caused by the insertion of a foreign object, it is preferable for the endoscopic probe to be as small as possible. Additionally, for non-medical applications, the ability to image within small conduits such as small ducts, pipes, tubing, and internal inspection through cracks and other tight spaces, etc., requires a probe of small size.
One useful medical probe employs spectrally encoded endoscopy (“SEE”), which is a miniature endoscopy technology that can conduct high-definition imaging through a sub-mm diameter probe. In a typical SEE probe, broadband light is diffracted by a grating at the distal end of an optical fiber to produce a dispersed spectrum of different wavelengths (colors) on a sample. Light returned from the sample is detected using a spectrometer; and each resolvable wavelength corresponds to reflectance from a different point on the sample. Thus, a SEE probe encodes light reflected from a given point in the sample by wavelength. The principle of the SEE technique and a SEE probe with a diameter of 0.5 mm (500 μm) have been described by D. Yelin et al., in a publication entitled “Three-dimensional miniature endoscopy”, Nature Vol. 443, 765-765 (2006). Another similar example is described by G. Tearney et al., in “Spectrally encoded miniature endoscopy”, Opt. Lett., 27(6): p. 412-414, 2002. Imaging with SEE can produce high-quality images in two- and three-dimensions.
Spectrally-encoded endoscopy utilizes the ability of the diffraction grating that deflects incident light to a diffraction angle according to wavelength. When the deflected light hits an object, light is scattered by the object. Detecting the scattered light intensity at each wavelength is equivalent to detecting the intensity from the corresponding diffraction angle. Thus, a one-dimensional, line image of the object can be obtained. A two-dimensional image is obtained by rotating the SEE probe. A three-dimensional image can be obtained by rotating and translating (moving linearly) the SEE probe. Moreover, when incorporated into a sample arm of an interferometer, the SEE probe can also acquire depth information from a sample (e.g., tissue).
Spectrally-encoded endoscopy probes are designed with side-viewing or forward-viewing characteristics. Forward view SEE probes are preferable for many applications. Forward view SEE imaging is particularly advantageous for applications such as orthopedics, ear, nose and throat (ENT), laparoscopy, and pediatric surgery. The forward-viewing (or front-view) probe type consists of multiple components including lenses, spacer elements, prisms and gratings, which makes the probe design complicated. Examples of such designs can be found, for example, in C. Pitris et al., Optical Express Vol. 11 120-124 (2003) and U.S. Pat. No. 8,145,018, both of which disclose a dual prism configuration where a grating is sandwiched between two prisms (a “grism”). The grism directs spectrally dispersed light such that at least one of the wavelengths propagates parallel to the optical axis of the probe. The grism consists of multiple components (grating, prisms) which need proper alignment. The need of a grism to construct a forward-view probe increases the cost, complexity of fabrication and size of the probe. Publication WO2015/116951 discloses another forward view endoscope where an angled reflective side surface makes the light incidence angle on the grating such that at least one of the wavelengths propagates parallel to the optical axis of the lens. However, these known designs of forward view SEE probes have drawbacks.
In particular, due to miniature size of the optics, the alignment of the spacer and the lens poses challenges during fabrication. Further, the illumination fiber is generally arranged off-axis to the GRIN lens, which introduces additional difficulties in fabrication as well as optical aberrations.
Accordingly, it can be beneficial to address and/or overcome at least some of the deficiencies indicated herein above, and thus to provide a new SEE probe having forward direction view, and an apparatus to use such a probe, e.g., for imaging in a small optics.